Как через Nginx проходят такие запросы?

upstream site {
    server localhost:8080;
}

map $http_upgrade $connection_upgrade {
    default upgrade;
    '' close;
}

server {
    listen       80;
    server_name  site.com;

    location / {
        root   /var/www/site/public;
        index  index.html index.htm;

        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;

        proxy_pass http://site/;
        proxy_redirect off;

        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
}